Spandex fibers for enhanced bonding

ABSTRACT

An elastic fiber is provided that includes polyurethane and/or polyurethaneurea and an additive such as polystyrene, an acrylic polymer, polyvinylpyrrolidone, copolymers thereof, derivatives thereof, and combinations thereof. The elastic fiber is useful in laminate structures, such as disposable hygiene articles as wells as in knit, woven and nonwoven fabric constructions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the formation of elastic fibers (eitherbicomponent such as spandex sheath-core fibers) or a single component(also referred to herein as monocomponent fiber) suitable for bonding toa substrate such as one includes polyolefin fiber. The spandex fibersare produced by dry spinning of polymer blends into a monocomponent orsheath-core bicomponent fiber.

2. Description of the Related Art

The global market for disposable diapers has an increased demand forfibers with excellent resilience, high stretchability and high bondingcapacity to nonwovens. Because of their outstanding properties,including high elongation and good elastic recovery, spandex fiberscontinue to gain interest for their use as elastic strands in disposablediapers. In incontinence products such as baby and adult diapers spandexfibers are used in several locations such as in leg bands and/orwaistbands to provide an excellent fit of the diapers.

To introduce stretchable regions in disposable diapers, a hot meltadhesive is applied against a stretched elastomeric fiber which is laterlaminated between two or more layers such as films or nonwovens that mayinclude polypropylene. While hot melt adhesives are applied to createbond sites between elastomeric strands and nonwoven substrates,significant lack of adhesion is still observed between the differentcomponents of the diaper: spandex strands, hot melt adhesive andnonwoven fabrics. It is believed that hot melt adhesives are compatiblewith nonwoven fabrics, while they are chemically incompatible withspandex fibers.

To address this drawback, the most popular method available for bondingspandex fibers to nonwoven fabrics is to overload spandex strands with ahot melt adhesive. Since the cost of hot melt adhesives is high, it isconvenient to apply adhesive add-ons lower than 18 gsm (grams ofadhesive material per square meter of substrate covered by theadhesive), more preferably equal to or lower than 15 gsm, and mostpreferably equal to or lower than 12 gsm.

U.S. Pat. No. 7,255,820 discloses the use of polystyrene in spandex, butonly for the purpose of achieving improved heat set, which is unrelatedto the technical problem disclosed herein.

SUMMARY OF THE INVENTION

Blend spinning spandex with an economical alternative polymer additiveprovides a route to reduce adhesive consumption cost with no change inspandex fibers performance. Of the unique benefits sheath-core fibersarrangement have over the conventional one, is a potential cost savingsassociated with the use of less of a more expensive polymeric additiveto obtain the same desirable characteristics or adding an expensiveadditive to only the sheath polymer, taking advantage of the lowermelting point of a polymer spun in the sheath to promote bonding withouta disruption in the morphology of the core component, improving theefficiency of elastic fibers made from a spinnable polymer core sheathedwithin a polymer blend comprising polymers with poor and goodspinnability.

Some embodiments provide monocomponent and/or bicomponent sheath-corespandex fibers with bonding enhancing additives which enhance bondingbetween spandex fibers to substrates, such as nonwovens. The sheath-corefibers include a higher-melting polyurethaneurea core and a sheathincluding a low-melting thermoplastic polymer as a bonding enhancingadditive.

The reason for using low-melting polymer sheath is to provide a higherbonding strength with adhesives and substrates such as nonwovens or, inthe alternative, to reduce the amount of adhesive required for the samebonding strength.

In one embodiment the elastic material is attached to the polyolefinnonwoven substrate when the melt adhesive is sprayed onto the elasticstrands at temperatures range 160° C.-200° C., which is above the glasstransition temperature of the thermoplastic polymer sheath, the lattermelts or softens the bonding enhancing additive to form bond sites withhot melt adhesives and nonwoven substrates upon cooling.

The thermoplastic binders include but not limited to polystyrene,acrylic polymer, polyvinylpyrrolidone, copolymers thereof, derivativesthereof and combinations thereof. The primary reason for usingpolystyrene polymers is that they are inherently capable of bonding tohot melt adhesive since these adhesives are mostly made of polystyreneblock copolymers. Finally, the low cost of polystyrene polymers isanother attractive reason to increases cost saving in disposable diapersapplications.

In one embodiment of a sheath-core elastic fiber, the core fibersinclude 100% of polyurethane such as a higher-melting segmentedpolyurethane/urea polymer and the sheath includes a polymer blendincluding about 30% to 99.5% of at least one selected polyurethane/ureapolymer and about 0.5% to about 70% of at least one additive such as anenhanced bonding additive. The elastic monocomponent and bicomponentsheath-core fibers are capable of providing enhanced bonding tosubstrates such as a polyolefin fiber substrate (including nonwovens)when the former are heated above the corresponding glass transition ormelting temperature of the enhanced bonding additive, optionally in thepresence of a hot melt adhesive. As an additional benefit, reduced tackof the fiber has been observed which improves over-end take-off tensionin dispenses spandex.

DETAILED DESCRIPTION OF THE INVENTION

Laminate structures are provided that include an elastic fiber includingpolyurethane and about 0.01% to about 30% by weight of at least oneadditive selected from the group consisting of a polystyrene, an acrylicpolymer, polyvinylpyrrolidone, copolymers thereof, derivatives thereof,and combinations thereof; where the elastic fiber is adhered to one ormore layers of a substrate selected from the group consisting of fabric,nonwoven, film, and combinations thereof. The laminate structure may beadhered by any known method, including but not limited to where theelastic fiber is adhered by an adhesive, ultrasonic bonding, thermalbonding or combinations thereof

The elastic fiber, which can be used in a fabrics or laminate structuresmay include a topical finish including mineral oil, silicon oil, orcombinations thereof. This finish may be present in any suitable amountsuch as an amount of 0.1% to about 2% by weight of the fiber includingup to about 1% by weight of the fiber. The topical finish has aviscosity of about 5 centistokes to about 150 centistokes.

Other additives can be included in the fiber as desired. Suitable fiberadditives include magnesium stearate, organic stearates, silicon oil,mineral oil, and combinations thereof.

The elastic fiber may include polyurethane and/or polyurethaneurea andabout 0.01% to about 0.90% (including about 0.3% to about 0.85% andabout 0.60% to about 0.85%) by weight of at least one additive selectedfrom the group consisting of a polystyrene, an acrylic polymer,copolymers thereof, derivatives thereof, and combinations thereof. Thisfiber may be solution-spun. The fiber may have a homogeneouscross-section (a monocomponent fiber) or have a bicomponent elasticfiber comprising a sheath-core construction; where the core includespolyurethane and said sheath comprises at least one additive selectedfrom the group consisting of a polystyrene, an acrylic polymer,polyvinylpyrrolidone, copolymers thereof, derivatives thereof, andcombinations thereof.

The elastic fiber may also be included in fabric, such as a knit, awoven, or a nonwoven construction. The elastic fiber includespolyurethane and about 0.01% to about 30% by weight of at least oneadditive selected from the group consisting of a polystyrene, an acrylicpolymer, polyvinylpyrrolidone, copolymers thereof, derivatives thereof,and combinations thereof.

A method for preparing a laminate structure is provided including:

-   -   providing an elastic fiber including polyurethane and about        0.01% to about 30% (such as about 0.1% to about 3.0%) by weight        of at least additive selected from the group consisting of a        polystyrene, an acrylic polymer, polyvinylpyrrolidone ,        copolymers thereof, derivatives thereof, and combinations        thereof;    -   where the elastic fiber is adhered to one or more layers of a        substrate selected from the group consisting of fabric,        nonwoven, film, and combinations thereof.

The laminate structure may be adhered by ultrasonic bonding, anadhesive, thermal bonding, and combinations thereof. This laminatearticle may be included in a disposable hygiene article.

Polyurethaneurea and Polyurethane Compositions

Polyurethaneurea compositions useful for preparing fiber or long chainsynthetic polymers that include at least 85% by weight of a segmentedpolyurethane. Typically, these include a polymeric glycol or polyolwhich is reacted with a diisocyanate to form an NCO-terminatedprepolymer (a “capped glycol”), which is then dissolved in a suitablesolvent, such as dimethylacetamide, dimethylformamide, orN-methylpyrrolidone, and then reacted with a difunctional chainextender. Polyurethanes are formed when the chain extenders are diols(and may be prepared without solvent). Polyurethaneureas, a sub-class ofpolyurethanes, are formed when the chain extenders are diamines. In thepreparation of a polyurethaneurea polymer which can be spun intospandex, the glycols are extended by sequential reaction of the hydroxyend groups with diisocyanates and one or more diamines. In each case,the glycols must undergo chain extension to provide a polymer with thenecessary properties, including viscosity. If desired, dibutyltindilaurate, stannous octoate, mineral acids, tertiary amines such astriethylamine, N,N′-dimethylpiperazine, and the like, and other knowncatalysts can be used to assist in the capping step.

Suitable polyol components include polyether glycols, polycarbonateglycols, and polyester glycols of number average molecular weight ofabout 600 to about 3,500. Mixtures of two or more polyols or copolymerscan be included.

Examples of polyether polyols that can be used include those glycolswith two or more hydroxy groups, from ring-opening polymerization and/orcopolymerization of ethylene oxide, propylene oxide, trimethylene oxide,tetrahydrofuran, and 3-methyltetrahydrofuran, or from condensationpolymerization of a polyhydric alcohol, such as a diol or diol mixtures,with less than 12 carbon atoms in each molecule, such as ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol 1,6-hexanediol,neopentyl glycol, 3-methyl-1,5-pentanediol, 1,7-heptanediol,1,8-octanediol, 1,9-nonanediol, 1,10-decanediol and 1,12-dodecanediol. Alinear, bifunctional polyether polyol is preferred, and apoly(tetramethylene ether) glycol of molecular weight of about 1,700 toabout 2,100, such as Terathane® 1800 (INVISTA of Wichita, Kans.) with afunctionality of 2, is one example of a specific suitable polyol.Co-polymers can include poly(tetramethylene-co-ethyleneether) glycol.

Examples of polyester polyols that can be used include those esterglycols with two or more hydroxy groups, produced by condensationpolymerization of aliphatic polycarboxylic acids and polyols, or theirmixtures, of low molecular weights with no more than 12 carbon atoms ineach molecule. Examples of suitable polycarboxylic acids are malonicacid, succinic acid, glutaric acid, adipic acid, pimelic acid, subericacid, azelaic acid, sebacic acid, undecanedicarboxylic acid, anddodecanedicarboxylic acid. Examples of suitable polyols for preparingthe polyester polyols are ethylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol 1,6-hexanediol, neopentyl glycol,3-methyl-1,5-pentanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol and 1,12-dodecanediol. A linearbifunctional polyester polyol with a melting temperature of about 5° C.to about 50° C. is an example of a specific polyester polyol.

Examples of polycarbonate polyols that can be used include thosecarbonate glycols with two or more hydroxy groups, produced bycondensation polymerization of phosgene, chloroformic acid ester,dialkyl carbonate or diallyl carbonate and aliphatic polyols, or theirmixtures, of low molecular weights with no more than 12 carbon atoms ineach molecule. Examples of suitable polyols for preparing thepolycarbonate polyols are diethylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol,3-methyl-1,5-pentanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol and 1,12-dodecanediol. A linear,bifunctional polycarbonate polyol with a melting temperature of about 5°C. to about 50° C. is an example of a specific polycarbonate polyol.

The diisocyanate component can also include a single diisocyanate or amixture of different diisocyanate including an isomer mixture ofdiphenylmethane diisocyanate (MDI) containing 4,4′-methylene bis(phenylisocyanate) and 2,4′-methylene bis(phenyl isocyanate). Any suitablearomatic or aliphatic diisocyanate can be included. Examples ofdiisocyanates that can be used include, but are not limited to,1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene,1-isocyanato-2-[(4-cyanatophenyl)methyl]benzene,bis(4-isocyanatocyclohexyl)methane,5-isocyanato-1-(isocyanatomethyl)-1,3,3-trimethylcyclohexane,1,3-diisocyanato-4-methyl-benzene, 2,2′-toluenediisocyanate,2,4′-toluenediisocyanate, and mixtures thereof. Examples of specificpolyisocyanate components include Mondur® ML (Bayer), Lupranate® MI(BASF), and Isonate® 50 O, P′ (Dow Chemical), and combinations thereof.

A chain extender may be either water or a diamine chain extender for apolyurethaneurea. Combinations of different chain extenders may beincluded depending on the desired properties of the polyurethaneurea andthe resulting fiber. Examples of suitable diamine chain extendersinclude: hydrazine; 1,2-ethylenediamine; 1,4-butanediamine;1,2-butanediamine; 1,3-butanediamine; 1,3-diamino-2,2-dimethylbutane;1,6-hexamethylenediamine; 1,12-dodecanediamine; 1,2-propanediamine;1,3-propanediamine; 2-methyl-1,5-pentanediamine;1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane;2,4-diamino-1-methylcyclohexane; N-methylamino-bis(3-propylamine);1,2-cyclohexanediamine; 1,4-cyclohexanediamine;4,4′-methylene-bis(cyclohexylamine); isophorone diamine;2,2-dimethyl-1,3-propanediamine; meta-tetramethylxylenediamine;1,3-diamino-4-methylcyclohexane; 1,3-cyclohexane-diamine;1,1-methylene-bis(4,4′-diaminohexane);3-aminomethyl-3,5,5-trimethylcyclohexane; 1,3-pentanediamine(1,3-diaminopentane); m-xylylene diamine; and Jeffamine® (Texaco).

When a polyurethane is desired, the chain extender is a diol. Examplesof such diols that may be used include, but are not limited to, ethyleneglycol, 1,3-propanediol, 1,2-propylene glycol, 3-methyl-1,5-pentanediol,2,2-dimethyl-1,3-trimethylene diol, 2,2,4-trimethyl-1,5-pentanediol,2-methyl-2-ethyl-1,3-propanediol, 1,4-bis(hydroxyethoxy)benzene, and1,4-butanediol and mixtures thereof.

A blocking agent which is a monofunctional alcohol or a monofunctionaldialkylamine may optionally be included to control the molecular weightof the polymer. Blends of one or more monofunctional alcohols with oneor more dialkylamine may also be included.

Examples of monofunctional alcohols useful with the present inventioninclude at least one member selected from the group consisting ofaliphatic and cycloaliphatic primary and secondary alcohols with 1 to 18carbons, phenol, substituted phenols, ethoxylated alkyl phenols andethoxylated fatty alcohols with molecular weight less than about 750,including molecular weight less than 500, hydroxyamines, hydroxymethyland hydroxyethyl substituted tertiary amines, hydroxymethyl andhydroxyethyl substituted heterocyclic compounds, and combinationsthereof, including furfuryl alcohol, tetrahydrofurfuryl alcohol,N-(2-hydroxyethyl)succinimide, 4-(2-hydroxyethyl)morpholine, methanol,ethanol, butanol, neopentyl alcohol, hexanol, cyclohexanol,cyclohexanemethanol, benzyl alcohol, octanol, octadecanol,N,N-diethylhydroxylamine, 2-(diethylamino)ethanol,2-dimethylaminoethanol, and 4-piperidineethanol, and combinationsthereof.

Examples of suitable mono-functional dialkylamine blocking agentsinclude: N,N-diethylamine, N-ethyl-N-propylamine, N,N-diisopropylamine,N-tert-butyl-N-methylamine, N-tert-butyl-N-benzylamine,N,N-dicyclohexylamine, N-ethyl-N-isopropylamine,N-tert-butyl-N-isopropylamine, N-isopropyl-N-cyclohexylamine,N-ethyl-N-cyclohexylamine, N,N-diethanolamine, and2,2,6,6-tetramethylpiperidine.

Bonding Enhancing Additives

The bonding enhancing additives may be any suitable hydrocarbon resinsuch as those selected from polystyrene, acrylic polymer,polyvinylpyrrolidone, copolymers thereof, derivatives thereof, andcombinations thereof. Derivatives can include esters, acids, amides, andthe like. The bonding enhancing additives may be of any suitablemolecular weight such as number average molecular weight of 300 to500,000. A higher number average molecular weight may be 50,000-500,000or 150,000 to 300,000. A lower number average molecular weight may beless than 50,000. Suitable ranges for the lower number average molecularweight hydrocarbon resin may be about 300 to 45,000 or 1000 to 40,000.

The styrene additive may include polystyrene, polystyrene copolymers,polystyrene derivatives, and combinations thereof. Examples of suitablestyrene-based polymers include, but are not limited to, polystyrene,p-alkylpolystyrene, such as p-methylpolystyrene, p-arylpolystyrene andthe like. Further, the example of the polystyrene copolymer includesstyrene-acrylonitrile copolymer (SAN), styrene-butadiene copolymer(SBS), styrene-butadiene block copolymer, acrylonitrile-butadienestyrenecopolymer (ABS), styrene co-polymer with (1-methylethenyl)benzene, andcombinations thereof.

The acrylic polymer may include any of a variety of monomers. Asmonomers, those including an acryl moiety, for example acrylic acid andmethacrylic acid, as well as their derivatives or mixtures thereof, aresuitable. Esters, amides, acrylic acid nitrile and their mixtures areconsidered preferably as derivatives. Examples include poly(butylmethacrylate), poly(ethyl methacrylate), poly(methyl methacrylate),polyacrylonitrile, poly(methyl methacrylate-co-butyl methacrylate), andcombinations thereof.

Examples of C₁₋₁₂ hydrocarbon group-containing (meth)acrylic acid estermonomer as component include (meth)acrylic acid alkyl esters,(meth)acrylic acid alkenyl esters, (meth)acrylic acid cycloalkyl esters,(meth)acrylic acid cycloalkenyl esters, (meth)acrylic acid aryl esters,(meth)acrylic acid alkylaryl esters, (meth)acrylic acid aralkyl esters,(meth)acrylic acid alkylaralkyl esters, (meth)acrylic acid aralkylarylesters, and the like. Among these, (meth)acrylic acid alkyl esters and(meth)acrylic acid cycloalkyl esters are suitable.

Examples of useful acrylic polymers include poly(butyl methacrylate),poly(ethyl methacrylate), poly(methyl methacrylate), polyacrylonitrile,poly(methyl methacrylate-co-butyl methacrylate), and combinationsthereof.

Additives

Classes of additives that may be optionally included in polyurethaneureacompositions are listed below. An exemplary and non-limiting list isincluded. However, additional additives are well-known in the art.Examples include: anti-oxidants, UV stabilizers, colorants, pigments,cross-linking agents, phase change materials (paraffin wax),antimicrobials, minerals (i.e., copper), microencapsulated additives(i.e., aloe vera, vitamin E gel, aloe vera, sea kelp, nicotine,caffeine, scents or aromas), nanoparticles (i.e., silica or carbon),calcium carbonate, flame retardants, antitack additives, chlorinedegradation resistant additives, vitamins, medicines, fragrances,electrically conductive additives, dyeability and/or dye-assist agents(such as quaternary ammonium salts). Other additives which may be addedto the polyurethaneurea compositions include adhesion promoters,anti-static agents, anti-creep agents, optical brighteners, coalescingagents, electroconductive additives, luminescent additives, lubricants,organic and inorganic fillers, preservatives, texturizing agents,thermochromic additives, insect repellants, and wetting agents,stabilizers (hindered phenols, zinc oxide, hindered amine), slipagents(silicone oil) and combinations thereof.

The additive may provide one or more beneficial properties including:dyeability, hydrophobicity (i.e., polytetrafluoroethylene (PTFE)),hydrophilicity (i.e., cellulose), friction control, chlorine resistance,degradation resistance (i.e., antioxidants), adhesiveness and/orfusibility (i.e., adhesives and adhesion promoters), flame retardance,antimicrobial behavior (silver, copper, ammonium salt), barrier,electrical conductivity (carbon black), tensile properties, color,luminescence, recyclability, biodegradability, fragrance, tack control(i.e., metal stearates), tactile properties, set-ability, thermalregulation (i.e., phase change materials), nutriceutical, delustrantsuch as titanium dioxide, stabilizers such as hydrotalcite, a mixture ofhuntite and hydromagnesite, UV screeners, and combinations thereof.

Process of Making Fibers

The fiber of some embodiments is produced by solution spinning (eitherwet-spinning or dry spinning) of the polyurethane-urea polymer from asolution with conventional urethane polymer solvents (e.g., DMAc). Thepolyurethaneurea polymer solutions may include any of the compositionsor additives described above. The polymer is prepared by reacting anorganic diisocyanate with appropriate glycol, at a mole ratio ofdiisocyanate to glycol in the range of 1.6 to 2.3, preferably 1.8 to2.0, to produce a “capped glycol”. The capped glycol is then reactedwith a mixture of diamine chain extenders. In the resultant polymer, thesoft segments are the polyether/urethane parts of the polymer chain.These soft segments exhibit melting temperatures of lower than 60° C.The hard segments are the polyurethane/urea parts of the polymer chains;these have melting temperatures of higher than 200° C. The hard segmentsamount to 5.5 to 9%, preferably 6 to 7.5%, of the total weight of thepolymer.

In one embodiment of preparing fibers, the polymer solutions containing30-40% polymer solids are metered through desired arrangement ofdistribution plates and orifices to form filaments. Distribution platesare arranged to combine polymer streams in a one of concentricsheath-core, eccentric sheath-core, and side-by-side arrangementfollowed by extrusion thru a common capillary. Extruded filaments aredried by introduction of hot, inert gas at 300° C.-400° C. and agas:polymer mass ratio of at least 10:1 and drawn at a speed of at least400 meters per minute (preferably at least 600 m/min) and then wound upat a speed of at least 500 meters per minute (preferably at least 750m/min). All examples given below were made with 80° C. extrusiontemperature in to a hot inert gas atmosphere at a take-up speed of 762m/min. Standard process conditions are well-known in the art.

The additive which enhances bonding, such as polystyrene, an acrylicpolymer, or polyvinylpyrrolidone may be added to the polymer solutionfor the core, the sheath only, or for a monocomponent (not bicomponent)fiber. For example, in a sheath-core bicomponent fiber, the additive maybe present only in the sheath. When the additive is only in the sheath,it may be present in an amount of about 0.5% to about 70% by weight ofthe sheath.

Yarns formed from elastic fibers made in accordance with the presentinvention generally have a tenacity at break of at least 0.6 cN/dtex, abreak elongation of at least 400%, an unload modulus at 300% elongationof at least 27 mg/dtex.

Strength and elastic properties of the spandex were measured inaccordance with the general method of ASTM D 2731-72. For the examplesreported in Tables below, spandex filaments having a 5 cm gauge lengthwere cycled between 0% and 300% elongation at a constant elongation rateof 50 cm per minute. Modulus was determined as the force at 100% (M100)and 200% (M200) elongation on the first cycle and is reported in grams.Unload modulus (U200) was determined at 200% elongation on the fifthcycle and is reported in the Tables in grams. Percent elongation atbreak and force at break was measured on the sixth extension cycle.

Percent set was determined as the elongation remaining between the fifthand sixth cycles as indicated by the point at which the fifth unloadcurve returned to substantially zero stress. Percent set was measured 30seconds after the samples had been subjected to five 0-300%elongation/relaxation cycles. The percent set was then calculated as %Set=100(Lf−Lo)/Lo, where Lo and Lf are the filament (yarn) length, whenheld straight without tension, before (Lo) and after (Lf) the fiveelongation/relaxation cycles.

The features and advantages of the present invention are more fullyshown by the following examples which are provided for purposes ofillustration, and are not to be construed as limiting the invention inany way.

EXAMPLES

Representative embodiments of the present invention will be describedwith reference to the following examples that illustrate the principleand practice of the present invention. In these examples,Polyurethane/urea prepared according to a conventional method is alinear polymer (commercially available from Invista, S. a. r. L., ofWichita, Kans. and Wilmington, Del.);

St stands for polystyrene;

St1 stands for lower number average molecular weight polystyrene;

BM stands for poly(butyl methacrylate);

IBM stands for poly(isobutyl methacrylate);

MMA stands for poly(methyl methacrylate);

AN stands for polyacrylonitrile;

SMMA stands for copolymer poly(styrene-co-methyl methacrylate);

SAN stands for copolymer poly(styrene-co-acrylonitrile);

PVP stands for polyvinylpyrrolidone

MB2766: thermoplastic acrylic resin

ZeroCreep™ stands for hot melt elastic attachment adhesive.

The compounds listed above are commercially available from the SigmaAldrich) except for MB2766 and ZeroCreep™ which were provided by DianalAmerica, Inc and the hot melt adhesive by Bostik.

Example 1

Core Solution

Segmented polyurethane was completely dissolved in a dimethylacetamidesolvent, to obtain a spinning core solution. As such, a mixing ratio byweight of polyurethane to DMAC was 35:65 (w/w).

Sheath solution

Polystyrene was completely dissolved in a dimethylacetamide solvent, toobtain a polystyrene stock solution, which was then mixed with asegmented polyurethane solution (see core solution). As such, a mixingratio by weight of polystyrene to polyurethane is listed in Table 1. Toassure uniformity, each copolymer sample was thoroughly mixed for 6hbefore characterization or spinning was started.

Thereafter, the core-sheath solutions were spun into a single thread of40 and 360 denier yarns with 4 filaments twisted together at a wound-upspeed of 930 meters per minute. Prior to entering the spinningcore-sheath cell, which was flushed with nitrogen gas of 375° C. at aflow rate of 5.5 kg per hour, the polymer solution temperature wascontrolled at 50° C. The dried yarn was then winding-up into a tube. Theas-spun yarn properties of this test item were measured and listed inTable 1.

Example 2

The same procedures and conditions were used as described in Example 1except that polystyrene was replaced either by poly(methyl methacrylate)or poly(acrylonitrile) and a mixing ratio by weight (w/w) shown inTable 1. The as-spun yarn properties of this test item were measured andlisted in Table 1.

Example 3

Polystyrene was dissolved in a dimethylacetamide solvent, to obtain apolystyrene solution (30%) and the formed polymer solution was spun intoa yarns. The as-spun yarn properties of this test item were measured andlisted in Table 3a.

Example 4

Both polystyrene and polyvinylpyrrolidone were separately dissolved in adimethylacetamide solvent, to obtain a polystyrene solution (30%) and apolyvinylpyrrolidone solution (20%). Thereafter, a polymer blendsolutions made from a polystyrene solution (30%) andpolyvinylpyrrolidone solution (20%) were spun into a yarns. The as-spunyarn properties of this test item were measured and listed in Table 3.

Example 5

Lower average number molecular weight polystyrene was dissolved in adimethylacetamide solvent, to obtain a polystyrene solution (60%) andthe formed polymer solution was spun into a yarns. The as-spun yarnproperties of this test item were measured and listed in Table 3b

TABLE 1 Comparison of sheath-core spandex as-spun yarn properties withcontrol spandex yarn. Sample Number P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11P12 Sheath PUU PUU/St PUU/St PUU/St PUU/St/ PUU/ PUU/ PUU PUU/St PUU/PUU/ PUU/ Polymer Type PU SMMA SAN BM IBM MB2766/St Weight 0 5 5 5 5 5 50 5 5 5 5 percentage of Sheath in fiber (%) Sheath 0 98.25/1.75 90/1070/30 40/30/30 90/10 90/10 0 80/20 80/20 80/20 80/10/10 Composition (%)Core Polymer PUU PUU PUU PUU PUU PUU PUU PUU PUU PUU PUU PUU TypeThermoplastic 0 0.09 0.5 1.5 3 0.5 0.5 0 1 1 1 1 polymer in fiber (%)Denier 369 379 338 363 364 368 374 370 368 372 369 369.4 ELO 500 519 524520 510 537 537 531 540 530 506 529 SET 26.5 26.8 27 29.3 28.8 28 2926.7 27.6 28.2 28.5 28.1 PUU: Control spandex yarn (polyurethaneurea);PU: Polyurethaneurea; St: Polystyrene; SMMA: Poly(styrene-co-methylmethacrylate); SAN: Poly(styrene-co-acrylonitrile); BM: Poly(butylmethacrylate); IBM: Poly(isobutyl methacrylate); MB2766: Acrylic resins.

Table 1 illustrates the properties of the sheath-core bicomponentspandex fibers suitable to the present invention. While P1 is thecontrol, the regular spandex, samples P2-10 are sheath-core spandexfibers made according to the present invention. It can be seen from theabove examples that dry spinning of a solution mixture of a segmentedpolyurethane with polymeric additive including but not limited topolystyrene, poly(styrene-co-methyl methacrylate);poly(styrene-co-acrylonitrile), poly(butyl methacrylate) and derivativeshas no significant negative impact to the yarn properties. The slightdeviations seen in the elongation and set data of these fibers wereexpected and they are attributable to the addition of polymericadditives into the individual spandex yarns.

Overall, the sheath-core bicomponent spandex fibers P2-10 were found tohave excellent properties such as high elongation and similar set to theregular spandex, P1.

Bonding Results

After bonding the bicomponent spandex fibers to nonwovens, the sampleswere tested for bond retention (100-% Creep Retention) according to themethod described earlier. In a diaper application, bond performance forspandex fibers is said to be good typically when the bond retention iseither more than 60%, preferably more than 70%, more preferably morethan 75%, most preferably more than 80% in a specific test describedhereinafter when it is done within 2 days after hot melt adhesive hasbeen applied on substrates. These tests are indicative of what level ofadhesion and bond retention can be achieved by a hot melt adhesive.Because of the high cost of hot melt adhesives, the adhesives are usedin an add-on amount lower than 18 gsm (grams of adhesive material persquare meter of substrate covered by the adhesive material), morepreferably equal to or lower than 15 gsm, and most preferably equal toor lower than 12 gsm, U.S. Pat. No. 20090264580.

In the present invention, the bond performance of sheath-core spandexfibers is illustrated by the specific examples shown in Table 2a-b.

TABLE 2a-b Comparison in bonding retention of sheath-core spandexas-spun yarn properties with control spandex yarn using 7, 11, and 15.5gsm of ZeroCreep ™ add-ons. Adhesive Adhesive Adhesive add-on add-onadd-on (gsm) % Bond (gsm) % Bond (gsm) % Bond 7 gsm retention 11 gsmretention 15.5 gsm retention a) P1 50.0 P1 65.0 P1 82.0 P2 59.0 P2 77.0P2 85.0 P3 67.0 P3 74.0 P3 84.0 P4 66.0 P4 78.0 P4 85.0 P5 65.0 P5 76.0P5 85.0 P6 57.0 P6 79.0 P6 83.0 P7 63.0 P7 77.0 P7 84.0 b) P8 67.0 P875.0 P8 86.0 P9 74.0 P9 82.0 P9 88.0 P10 72.0 P10 80.0 P10 86.0 P11 74.0P11 79.0 P11 88.0 P12 75.0 P12 82.0 P12 88.0

From Table 2a-b, it is clear that the inventive bicomponent fibersexhibited greater bond retention to nonwoven fabrics than the controlspandex fiber.

When the ZeroCreep™ add-on is 7 gsm, the bicomponent spandex fibers P2-7and P9-12 display good bond performance than the control spandex fibersP1 or P8 (Table 2a-b). It should be noted that fibers with polystyreneand poly(butyl methacrylate) additives display higher bond retention.

At ZeroCreep™ add-on equivalents to 11 gsm, all six bicomponent fibersclaimed by the present invention have superior bondability to nonwovensthan the control spandex fiber. As seen previously, the bond retentionincreased more when polystyrene and poly(butyl methacrylate) are used infibers sheath.

When the ZeroCreep™ add-on is 15.5 gsm, all inventive fibers (P2-7 andP9-12) including the control ones (P1 and P8) exhibited much higher bondretention. Still, the inventive bicomponent fibers display a bettercreep retention compared to the control fiber.

TABLE 3a Comparison of monocomponent spandex as-spun yarn propertieswith control spandex yarn. Sample Number P13 P14 P15 Polymer PUU1PUU1/St PUU1/St/PVP Type Thermoplastic 0 0.875 98.25/0.875/0.875 polymerin fiber (%) Denier 745.5 739.5 NA ELO 492.75 520.25 500.0 TEN 423.8522.45 409.8 TP2 81.06 83.72 97.71 TM2 16.55 15.96 15.07 SET 25.55 27.9528.5 PUU1: Control spandex yarn (polyurethaneurea); St: Polystyrene;PVP: polyvinylpyrrolidone.

TABLE 3b Comparison of monocomponent spandex as-spun yarn propertieswith control spandex yarn. Sample Number P16 P17 P18 Polymer PUU2/St1PUU2/St1 PUU2 Type Thermoplastic 2.5 4.2 0 polymer in fiber (%) TargetDenier 720 720 720 ELO 465 477 503 TEN 380 410 388 TP2 84.2 84.8 85.3TM2 15.7 15.4 15.3 SET 27.3 28.1 26.5 PUU2: Control spandex yarn(polyurethaneurea); St1: low average number molecular weight polystyrene

TABLE 4 Comparison in bonding retention of monocomponent spandex as-spunyarn properties with control spandex yarn using 7, 11, and 15.5 gsm ofZeroCreep ™ add-ons. Adhesive Adhesive Adhesive add-on add-on add-on(gsm) % Bond (gsm) % Bond (gsm) % Bond 7 gsm retention 11 gsm retention15.5 gsm retention P13 53.0 P13 80.0 P13 87.0 P14 63.0 P14 79.0 P14 87.0P15 58.0 P15 78.0 P15 84.0

TABLE 5 Comparison in bonding retention of monocomponent spandex as-spunyarn properties with control spandex yarn using 15 and 20 mg/m/strand ofTechnomelt ® DM 800B mady be Henkel. Adhesive Adhesive add-on % Bondadd-on % Bond 15 mg/m/strand retention 20 mg/m/strand retention P16 82.3P16 89.2 P17 83.5 P17 88.7 P18 77.6 P18 87.7

Tables 4 and 5 show the inventive fibers exhibit better bond retentionthan the control.

While there have been described what are presently believed to be thepreferred embodiments of the invention, those skilled in the art willrealize that changes and modifications may be made thereto withoutdeparting from the spirit of the invention, and it is intended toinclude all such changes and modifications as fall within the true scopeof the invention.

1. A laminate structure comprising: an elastic fiber comprisingpolyurethane and about 0.01% to about 30% by weight of at least oneadditive selected from the group consisting of a polystyrene, an acrylicpolymer, polyvinylpyrrolidone, copolymers thereof, derivatives thereof,and combinations thereof; wherein said elastic fiber is adhered to oneor more layers of a substrate selected from the group consisting offabric, nonwoven, film, and combinations thereof.
 2. The laminatestructure of claim 1, wherein said additive is selected frompolystyrene, polystyrene co-polymers, polystyrene derivatives, andcombinations thereof.
 3. The laminate structure of claim 1, wherein saidadditive is selected from polystyrene, styrene-acrylonitrile copolymer(SAN), styrene-butadiene copolymer (SBS), styrene-butadiene blockcopolymer, acrylonitrile-butadienestyrene copolymer (ABS), andcombinations thereof.
 4. The laminate structure of claim 1, wherein saidelastic fiber is adhered by an adhesive, ultrasonic bonding, thermalbonding or combinations thereof.
 5. The laminate structure of claim 1,wherein said elastic fiber is solution-spun.
 6. The laminate structureof claim 1, wherein said elastic fiber is a sheath-core bicomponentfiber and said additive is present only in said sheath.
 7. The laminatestructure of claim 6, wherein said sheath includes said additive in anamount of about 0.5% to about 70% by weight of said sheath.
 8. Thelaminate structure of claim 1, wherein said acrylic polymer is selectedfrom poly(butyl methacrylate), poly(ethyl methacrylate), poly(methylmethacrylate), polyacrylonitrile, poly(methyl methacrylate-co-butylmethacrylate), and combinations thereof.
 9. The laminate structure ofclaim 1, wherein said elastic fiber further comprises a topical finishcomprising mineral oil, silicon oil, or combinations thereof in anamount of 0.1% to about 2% by weight of the fiber.
 10. The laminatestructure of claim 9, wherein said topical finish has a viscosity ofabout 5 centistokes to about 150 centistokes.
 11. The laminate structureof claim 1, wherein said elastic fiber further comprises an additionaladditive selected from magnesium stearate, organic stearates, siliconoil, mineral oil, and combinations thereof.
 12. An elastic fibercomprising polyurethane and about 0.01% to about 0.90% by weight of atleast one additive selected from the group consisting of a polystyrene,an acrylic polymer, copolymers thereof, derivatives thereof, andcombinations thereof.
 13. An elastic fiber comprising polyurethane andat least one additive selected from the group consisting of apolystyrene, an acrylic polymer, copolymers thereof, derivativesthereof, and combinations thereof, wherein the additive has a numberaverage molecular weight of 300 to less than 50,000.
 14. The elasticfiber of claim 13, wherein the additive has a number average molecularweight of 300 to 45,000.
 15. A solution-spun bicomponent elastic fibercomprising a sheath-core construction; wherein said core comprisespolyurethane and said sheath comprises at least one additive selectedfrom the group consisting of a polystyrene, an acrylic polymer,polyvinylpyrrolidone, copolymers thereof, derivatives thereof, andcombinations thereof.
 16. A fabric comprising: an elastic fibercomprising polyurethane and about 0.01% to about 30% by weight of atleast one additive selected from the group consisting of a polystyrene,an acrylic polymer, polyvinylpyrrolidone, copolymers thereof,derivatives thereof, and combinations thereof.
 17. The fabric of claim16, wherein said fabric comprises a knit, woven or nonwovenconstruction.
 18. A method for preparing a laminate structurecomprising: providing an elastic fiber comprising polyurethane and about0.01% to about 30% by weight of at least additive selected from thegroup consisting of a polystyrene, an acrylic polymer,polyvinylpyrrolidone, copolymers thereof, derivatives thereof, andcombinations thereof; wherein said elastic fiber is adhered to one ormore layers of a substrate selected from the group consisting of fabric,nonwoven, film, and combinations thereof.
 19. The method of claim 18,wherein said elastic fiber is adhered by ultrasonic bonding, anadhesive, thermal bonding, and combinations thereof.
 20. The method ofclaim 18, wherein said laminate article is included in a disposablehygiene article.